Tim Dawson (02/05/2011)
At the moment, SkyDemon offers the same as most other VFR handhelds which is GPS altitude. Assuming a perfect fix, this is your actual altitude above local mean sea level.As soon as one switches to flying relative to another datum (1013.25 for example) SkyDemon, and any other GPS without access to static pressure information, can't really help you any more.I just wanted to follow up on this, in relation to another
thread I have just started on this topic.
GPS Navigation software built for glider pilots (SeeYou, XCSoar, LK8000, ... just to name a few) all let the pilot enter the current QNH, then work out the difference between Flight Level and GPS altitude (based on the difference between QNH and 1013.25 pressure levels), and display the "correct" airspace warnings regardless of whether the airspace is defined in terms of altitude or flight level.
When the device is connected to an instrument giving pressure altitude (eg. an IGC flight logger), this is all done automatically, but otherwise the pilot's QNH input is used.
I would really love to see SD do something similar, given that on a nice day we are quite likely to fly above the transition altitude.